A LED lamp refers to a lighting fixture that uses one or more LEDs as a main light source. The LED is a solid state semiconductor device, and different kinds of LEDs can emit light of different wavelengths with various colors. One of the recent developments in the LED technology is to apply fluorescent powder on a blue LED so as to transform the blue LED into a white LED. The LED lamp has small size and light weight, and is encapsulated with epoxy resin such that it has high mechanical impact and vibration strength and is not vulnerable to break. Moreover, the LED lamp has a long brightness decay time so that its lifespan could be as long as 50 to 100 thousand hours, which is much longer than that of a conventional tungsten lamp (about 1 thousand hours) and a fluorescent lamp (about 10 thousand hours). The lifetime of the LED lamp may last for 5 to 10 years, therefore the cost for changing lighting fixtures would be greatly reduced. In addition, the LED lamp can be driven to emit light even at a very small current and consumes about half the energy of the fluorescent lamp to provide the substantially same illumination effect. Hence, the LED lamp has the advantages of electricity and energy saving.
Presently, a single-chip or multi-chip package of high power LED, AC LED, or the like are widely used in a LED bulb lamp. The single-chip package of high power LED finds wide applications in lighting fixtures that require light concentration and/or strong direction of light such as MR16 or LED projection lamp. The multi-chip package of high power LED can be found as a light source in a LED bulb lamp with 10 watts or above that take the place of energy saving lamps.
The LED lighting fixture is structurally similar to a reflective energy saving lamp except for the use of LED as a light emitting element. In general, the LED lighting fixture comprises a LED lamp board having a LED chip package, a fluorescent powder layer and the like; a housing; a circuitry for powering the LED chip; a reflector cup; a heat sink; and the like. FIG. 1A illustrates a perspective view of a LED reflector lamp of the prior art; and FIG. 1B is a bottom view of the LED reflector lamp of the prior art with LEDs used as a light-emitting element which are positioned above a label plate at the base of the LED lamp. The LED chip is powered to emit light which is transmitted to the fluorescent powder applied on the LED chip or the package, and the fluorescent powder is excited to emit white light or light with a predetermined color. In this LED lighting fixture, light emits from two sides of an upper portion of the label plate as shown in FIG. 1A and then are reflected by the reflector cup to emit forward.
However, in use, such a prior art LED lighting fixture would produce an illumination pattern having annular yellow zones that affects the illumination uniformity. This results in poor quality of illumination of the LED lamp, and has an adverse effect on the visual effect and its applications.